This invention relates to optical fibers, and in particular, to structures for supporting optical fibers.
In an optical communication system, it is sometimes necessary for a beam of light to emerge from a source fiber into free space and to later enter a destination fiber. To accomplish this, the beam of light that emerges from the source fiber must be guided across the free space so that as much light as possible from that beam enters the destination fiber. The extent to which light emerging from the source fiber fails to enter the destination fiber is referred to as the xe2x80x9cinsertion loss.xe2x80x9d
The guiding of the beam of light across free space is typically accomplished by lenses and mirrors. These optical guiding elements must be precisely aligned relative to the source fiber, the destination fiber, and to each other. The extent to which this can be achieved depends, in part, on the extent to which an optical fiber can be precisely positioned.
Because an optical fiber is flexible, precise positioning of a fiber typically requires placing the fiber in a structure that securely engages it. One such structure is a mask having precisely placed holes formed thereon. When a fiber is inserted into a hole in such a mask, the wall forming the hole engages the fiber and fixes its location.
Inserting a flexible fiber into a hole is somewhat like threading a needle. The larger the hole is relative to the fiber, the easier it is to insert the fiber into the hole. However, to the extent that the hole is larger than the fiber, the walls forming the hole are unable to engage the fiber at a precisely fixed location.
The invention provides a fiber-locating structure having one or more passageways. Each passageway includes a funnel portion for receiving an optical fiber, and a tunnel portion for engaging the optical fiber. The fiber is easily inserted into the large opening of the funnel portion. The walls forming the funnel portion then guide the fiber into the narrower tunnel portion.
In one embodiment, the invention includes a fiber-locating structure having opposed first and second faces. A first wall, defining a funnel, extends from the first face toward the second face; while a second wall, defining a tunnel, extends from the second face toward the first face. The first and second walls are disposed such that the funnel and the tunnel meet to form a continuous passageway between the first face and the second face.
The tunnel portion can have any cross-section. In some embodiments, the cross-section of the tunnel portion is circular. However, the tunnel portion can also have protrusions extending radially inward and forming kinematic mounts for an optical fiber inserted therein.
In another embodiment, the invention also includes an optical fiber, such as a tapered optical fiber, extending from the first face to the second face through the funnel and the tunnel. As used herein, optical fibers are not restricted to those fibers that are intended to guide visible light.
The invention also includes a method for aligning an optical fiber by forming a funnel extending from a first face toward a second face of a fiber-locating structure and forming a tunnel extending from the second face toward the first face. The funnel and the tunnel are disposed to intersect within the interior of the fiber-locating structure, thereby forming a continuous passageway between the first face and the second face.
Some practices of the invention include forming the funnel portion by anisotropically etching the first face of the fiber-locating structure. This results in a pyramidal funnel portion. Other practices of the invention include forming the tunnel by deep reaction ion etching (xe2x80x9cDRIExe2x80x9d) the second face of the monolith. To better control the depths of the funnel and the tunnel, a stop layer can be incorporated into the interior of the fiber-locating structure. After etching to form a tunnel and a funnel on opposite sides of the stop layer, a portion of the stop layer separating the tunnel and the funnel is removed, thereby joining the tunnel to the funnel and forming a passageway between the first and second faces of the fiber-locating structure.
Additional practices of the invention include providing an optical fiber having a tapered end and inserting that tapered end into the funnel and through the tunnel. As the tapered end is inserted into the funnel, the walls of the funnel guide the tapered end into the tunnel.
In some cases, the mechanical strain at the point at which the fiber is supported introduces flaws into the fiber. To reduce the adverse effects of any flaws in the fiber, some practices of the invention include moving this contact point to a location in which it can easily be removed. One practice of the invention thus includes providing a scaffolding layer on the second face. This scaffolding layer extends part way into the tunnel, thereby forming a constricted transverse section within the tunnel. An optical fiber having a tapered end can then be inserted into the funnel and through the tunnel, until it is supported by the scaffolding layer within the constricted transverse section of the tunnel. After adhesively bonding the fiber to the walls forming the tunnel, the scaffolding layer is then removed and, optionally, a selected thickness of the second face of the monolith is also removed. This thickness is selected so that any flaw near the tip of the optical fiber is also removed.
This results in an optical fiber that is surrounded by the adhesive material and therefore less likely to be subjected to high local stresses.
In another practice of the invention, the scaffolding layer is a soft-metal layer. A tapered optical fiber is then inserted into the funnel and through the tunnel until its tapered end is seated against the soft-metal scaffolding layer. This soft-metal layer surrounds the optical fiber and constrains its movement while providing sufficient compliance to protect the optical fiber from excessive stresses arising from contact with the fiber-locating structure.
These and other features and advantages of the invention will be apparent from the following detailed description and the accompanying figures, in which: